Using human recombinant MIF from transfected COS-1 cells, we have shown that this lymphokine upregulates several macrophage molecules associated with activation (HLA-DR, IL-1beta, TNFalpha, and nitric oxide), activates macrophage to kill protozoa (intracellularly) and tumor cells (extracellularly), and enhances the clumping and adhesion of macrophages to each other. For controls, we used supernatants containing non-active "stopMIF" from COS-1 cells transfected with a mutated MIF-cDNA containing a stop codon. Human rMIF acts on murine cells in vitro, and when given with an antigen to mice in vivo, it elicits an antigen-dependent lymph node T cell proliferative response in as great as that elicited by complete Freund's adjuvant. Finally, preliminary studies show that the in vivo adjuvant effect of complete Freund's adjuvant is totally abrogated by antibodies to rMIF. The specific aims of this proposal are: 1. To produce and purify biologically active recombinant MIF in reasonable quantity. 2. To determine the mechanism of the adjuvant action of rMIF. This will include studies on the effect of rMIF on antigen processing, on integrin activity and expression, and on its interaction with other cytokines. 3. To ascertain the mechanism for the recent finding that, when given to mice, antibodies to rMIF abrogate the adjuvant action of complete Freund's adjuvant. 4. To use purified labelled rMIF to obtain the rMIF receptor, by direct receptor expression cloning or by immunochemical means.